Q: Repeat functions

I have a function A and I have declared what this function does.

I'd like that function to be repeated

For example,

I have 2 buttons called B and C

when the user click B do A and when the user click C do A as well

I only want to write the code for the function once

the code I want show look like this

A={1+2-3*4}

when B is clicked do A

when C is clicked do A

rather than this

when B is clicked do {1+2-3*4}

when C is clicked do {1+2-3*4}